Atrial fibrillation is a debilitating medical condition in which the upper chambers of the heart beat in a discoordinated fashion. This can lead to palpitations, breathlessness, fatigue, and stroke. A treatment method that has rapidly gained acceptance as the primary procedure to cure atrial fibrillation is radiofrequency (RF) catheter ablation of the regions in the heart that cause the arrhythmia. Due to the close proximity of the heart and esophagus, RF catheter ablation can lead to life threatening damage to the esophagus since RF energy delivered to the heart can also affect the nearby esophageal tissue. The closer tissue is to a heat source, like an RF therapy site, the more heat is delivered to the tissue since heat flux rate varies as the reciprocal of the square of the radial difference between the tissue and the heat source. Thus, the closeness of the esophagus to the heart causes it to receive a significant amount of heat from adjacent heat therapy sites. In its worst case, esophageal damage can lead to the formation of a connection between the heart and the esophagus, an atrio-esophageal fistula. Approximately 50% of patients suffering this complication die. With an estimated occurrence of up to 1% and nearly 150,000 expected RF ablations by 2010, esophageal damage represents a major threat to patient welfare and a significant burden on the healthcare system. Currently, there is no effective method to directly avoid this dreaded complication during atrial fibrillation ablation procedures without potentially affecting the efficacy of the procedure.
According to the 2002 Health Research International atrial fibrillation marketing report, the incidence of atrio-esophageal fistula formation is estimated to be between 0.5 and 1 percent. However, it is suspected that this number is greatly underreported. Doll and colleagues provide some evidence that the incidence is indeed higher; they reported 4 cases in a series of 129 patients (3.1%) receiving intraoperative RF ablation. Even given the low occurrence, atrio-esophageal fistula formation is a terrible complication with a very high mortality rate (50% mortality rate in reported occurrences). Other events associated with esophageal perforation include air embolism and stroke, endocarditis, mediastinitis, and severe gastrointestinal bleeding. Further morbidity results as patients often develop permanent neurological deficits from air emboli or develop sepsis from endocarditis. Additionally, even if outright fistula formation does not occur, damage to the vagus plexus surrounding the esophagus may give rise to pyloric spasm and gastric hypomobility. Since there have been no detailed studies that have consistently screened patients for esophageal injury after atrial fibrillation ablation, it is difficult to correctly estimate the actual number of patients who suffer non life-threatening esophageal damage during and after ablation. It is believed that esophageal damage during ablation is a severely under-reported phenomenon.
Esophageal damage is a devastating complication of atrial fibrillation ablation. There is no standard approach to prevent this complication. When ablating parts of the heart that are in the vicinity of the esophagus, physicians typically ablate tissue with great care, and often reduce the temperature or power of RF ablation. However, a recent study by Cummings J, Schweiket R, Saliba W, et al: in Circulation 112, 1524 (2005), suggests that there is little or no correlation between RF ablation power and esophageal temperature. Further, a low ablation/RF electrode temperature is likely to result in less effective lesions and therefore, a lower likelihood that the ablation procedure will be successful in the long-run. Moreover, the possibility of damaging the esophagus leads to increased operator anxiety; procedure time also increases due to the extreme care that needs to be taken when ablating in the posterior left atrium (LA) of the heart. Other modifications to the ablation procedure, such as moving posterior wall lesion locations or avoiding posterior lesions altogether, have been suggested, but again raise the possibility of degrading the efficacy of ablation. Further, the anatomic variability of the esophagus makes avoidance of lesions along its course difficult and complications persist.
In view of these shortcomings and challenges, there remains a need for an esophageal protection device for prevention of esophageal damage during therapy to maintain therapy efficacy while therapy is applied to a treatment site outside of but near the esophagus.